Apparatus for processing energy regenerated by an AC motor

ABSTRACT

An apparatus for processing the energy regenerated by an AC motor, which comprises a regeneration detection logic circuit (7) that produces a regeneration detection signal when the AC motor driving semiconductor switches are nonconductive and when the direction of the current flowing through the AC motor is opposite to that of the current when the AC motor is driven and a regeneration drive circuit 8 which drives the regenerated energy processing semiconductor switches responsive to the regeneration detection signal. The apparatus renders the regenerated energy processing semiconductor switches conductive so that the regenerated energy is returned to the AC power source only when the AC motor is in a regenerative condition. Therefore, electric power need be consumed in only small amounts by the resistors that protect the semiconductor switches for processing the regenerated energy, and the apparatus can be constructed so that it is small in size.

DESCRIPTION

1. FIELD OF THE ART

The present invention relates to an apparatus for processing energyregenerated by an AC motor and particularly to an apparatus whichreturns the energy regenerated by the AC motor to an AC power source.

2. BACKGROUND OF THE ART

The energy regenerated by a motor due to the inertial energy thereof orthe energy which the motor receives from an external source usuallyresults in the rise of potential of a DC power source to which isconnected a motor drive circuit that receives pulse width modulation(PWM) signals. The rise in potential often destroys a smoothingcapacitor which is contained in a rectifier circuit or semiconductorswitches are contained in the motor drive circuit to drive the AC motor.It is therefore necessary to process the regenerated energy by somemeans.

As one means for processing the regenerated energy, a system is knownwhich returns the regenerated energy to an AC power source.

In a conventional apparatus for returning the regenerated energy to theAC power source, hereinafter described in detail, voltages between thephases of the AC power source are monitored during the period ofdeceleration mode of the AC motor, and semiconductor switches forprocessing the regenerated energy are closed during periods in whichvoltages between the phases exceed a predetermined value so as to returnthe electric current of the DC power source to the AC power source. Theregenerated energy can be efficiently returned to the AC power source ifit is returned during the periods in which voltages between the phasesof the AC power source are great.

In the AC motor, however, three operation modes are performedrepetitively, i.e., regeneration, circulation, and consumption, and aregenerative condition is not always established even when voltagesbetween the phases are greater than a predetermined value during thedeceleration mode. As was mentioned above, since semiconductor switchesfor processing the regenerated energy are closed whenever the voltagesbetween the phases become greater than a predetermined value, a largeamount of electric power must be dissipated by resistors that areinserted, for protecting the semiconductor switches, between the linesof the DC power source and the semiconductor switches. For this purpose,the resistors must be capable of handling a large amount of electricpower. Because of this resistors for handling a large amount of electricpower are much greater in size than other elements and make theapparatus for processing the regenerated energy bulky.

DISCLOSURE OF THE INVENTION

IN view of the problems inherent in the above-mentioned conventionalapparatus, the object of the present invention, which is based on theidea of detecting the regenerative condition of an AC motor bymonitoring the direction of the current flowing through the AC motor andthe condition of the motor drive circuit, in addition to monitoring thedeceleration mode and the condition in which voltages between the phasesare greater than a predetermined value of the AC power source, toprovide an apparatus for processing energy regenerated by an AC motor,which apparatus instantaneously discriminates whether or not the ACmotor is in a regenerative condition and returns the regenerated energyto the AC power source only under a regenerative condition by renderingconductive the semiconductor switches for processing the regeneratedenergy, so that the power consumption is decreased in the resistors forprotecting the semiconductor switches for processing the regeneratedenergy, resulting in the possibility of reduced power in the resistorsand, accordingly, a reduction in the size of the apparatus forprocessing the regenerated energy.

To achieve the above-mentioned object, the present invention provides anapparatus for processing energy regenerated by an AC motor, whichcomprises: a rectifier circuit for supplying a direct current to thelines of the DC power source by rectifying an alternating currentsupplied from an AC power source; a drive circuit including AC motordriving semiconductor switches connected across the lines of the DCpower source, the semiconductor switches being rendered conductive uponthe receipt of a PWM signal when the AC motor is to be driven so as tosupply the electric current from the lines of the DC power source toeach of the phases of the AC motor; a regenerated energy processingcircuit connected across the lines of the DC power source, includingregenerated energy processing semiconductor switches for returning theenergy regenerated by the AC motor to the AC power source, and resistorsthat protect the semiconductor switches for processing the regeneratedenergy; current direction detectors for detecting the direction of thecurrent flowing through each of the phases of the AC motor; aregeneration detection logic circuit for producing a regenerationdetection signal when the semiconductor switches for driving the ACmotor are nonconductive and when the direction of the current detectedby the current direction detectors is opposite to the direction of thecurrent when the AC motor is driven; and a regeneration drive circuitfor driving the regenerated energy processing semiconductor switchesresponsive to the regeneration detection signal.

According to the above-mentioned apparatus for processing theregenerated energy of the present invention, the resistors forprotecting the regenerated energy processing semiconductor switches maybe one for reduced power consumption, and, hence, the size of theapparatus can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned object and features of the present invention will bemore apparent when read from the following description of an embodimentof the present invention in conjunction with the accompanying drawings,in which:

FIG. 1 is a block circuit diagram which schematically illustrates anapparatus for processing the energy regenerated by an AC motor accordingto an embodiment of the present invention;

FIG. 2 is a diagram of waveforms illustrating the operation of a phasedetector circuit 6 which is shown in FIG. 1;

FIG. 3 is a circuit diagram of a PWM drive circuit and an AC motor andexplains the principle for discriminating whether or not the AC motor isin a regenerative condition;

FIG. 4 is a diagram of a logic circuit illustrating a portion of theregeneration detection logic circuit of FIG. 1; and

FIG. 5 is a diagram which illustrates in detail a regeneration drivecircuit 8 which is shown in FIG. 1.

BEST MODE FOR PUTTING THE INVENTION INTO PRACTICE

An embodiment of the present invention is described below in conjunctionwith the drawings.

FIG. 1 is a block circuit diagram which schematically illustrates anapparatus for processing the energy regenerated by an AC motor accordingto an embodiment of the present invention. In FIG. 1, reference numeral1 denotes a three-phase AC power source, 2 denotes a rectifier circuit,3 denotes a circuit for processing the regenerated energy, 4 denotes adrive circuit for driving a motor responsive to PWM signals, and 5denotes a three-phase AC motor. The rectifier circuit 2 consists of sixdiodes and a smoothing capacitor C. The circuit 3 for processing theregenerated energy consists of NPN transistors Q₁ to Q₆ for processingthe regenerated energy and protection resistors R₁ and R₂ which preventa heavy current from flowing into the transistors Q₁ to Q₆. Thetransistors Q₁ and Q₂, Q₃ and Q₄, and Q₅ and Q₆ are connected in series,respectively. The collectors of the transistors Q₁, Q₃, and Q₅ areconnected to a DC power source line V_(D) via the protection resistorR₁. The emitters of the transistors Q₂, Q₄, and Q₆ are connected to aground line V_(E) via the protection resistors R₂. A drive signalobtained by the present invention is applied to the bases of thetransistors Q₁ to Q₆, whereby the regenerated energy is recovered fromthe DC power source line V_(D) into the AC power source 1 throughportions of the transistors Q₁ to Q₆ only when the AC motor 5 is in aregenerative condition.

The drive circuit 4 consists of six NPN transistors Q₇ to Q₁₂, whichreceive PWM signals that are obtained by pulse-width modulation of athree-phase alternating current, and diodes D₁ to D₆, the cathodes ofwhich are connected to the collectors of these transistors and theanodes of which are connected to the emitters of these transistors. PWMsignals R⁺, S⁺, and T⁺ are applied to the bases of the transistors Q₇,Q₉, and Q₁₁, respectively. PWM signals R⁻, S⁻, and T⁻ are applied to thebases of the transistors Q₈, Q₁₀, and Q₁₂, respectively. Here, thesignals R⁺ and R⁻, S⁺ and S⁻, and T⁺ and T⁻ are logic signals thatassume the level "0" when the other ones assume the level "1". Thediodes D₁ to D₆ permit the passage of a circulating current that flowsthrough the AC motor 5 and a current regenerated by the AC motor 5.

Reference numeral 6 denotes a circuit which detects the phase of thethree-phase AC power source 1 and which produces two drive signals amongthe drive signals A to F when voltages among the phases become greaterthan a predetermined value in the deceleration mode. In the conventionalapparatus, the drive signals A to F produced by the phase detectorcircuit 6 are applied directly to the bases of the transistors Q₁ to Q₆for processing the regenerated energy.

According to the present invention, provision is made for a regenerationdetection logic circuit 7 and a regeneration drive circuit 8.

The regeneration detection logic circuit 7 discriminates whether or notthe AC motor 5 is in a regenerative condition, relying upon the outputsof current direction detectors 10₁, 10₂, and 10₃ that detect thedirection of the current flowing through the AC motor 5 and upon the PWMsignals R⁺, R⁻, S⁺, S⁻, T⁺, and T⁻ applied to the bases of thetransistors in the drive circuit 4. When the AC motor 5 is in aregenerative condition, the regeneration detection logic circuit 7produces a regeneration detection signal.

The regeneration drive circuit 8 produces drive signals A' to F' todrive the transistors Q₁ to Q₆ for processing the regenerated energy,responsive to the drive signals A to F produced by the phase detectorcircuit 6 and the regeneration detection signal produced by theregeneration detection logic circuit 7.

According to the circuit construction of FIG. 1, drive signals areapplied to the transistors Q₁ to Q₆ for processing the regeneratedenergy only when the AC motor 5 is in a practically regenerativecondition. Therefore, electric power is consumed by the resistors R₁ andR₂ in the regenerated energy processing circuit 3 in amountsconsiderably smaller than the electric power that must be dissipated bythe conventional apparatus.

FIG. 2 is a diagram of waveforms illustrating the operation of the phasedetector circuit 6 of FIG. 1. In FIG. 2, the drive signals A and Dassume the logic level "1" during a period T₁ in which the voltage U-Vof the U-phase relative to the V-phase in the three-phase alternatingcurrent is greater than a predetermined value V₀. In the conventionalart, the drive signals A and D are directly applied to the bases of thetransistors Q₁ and Q₄ for processing the regenerated energy, and thecurrent is allowed to flow during the period T₁ from the DC power sourceline V_(D) to the ground line V_(E) via the resistor R₁, the transistorQ₁, the U-phase of the three-phase AC system, the V-phase of thethree-phase AC system, the transistor Q₄, and the resistor R₂ to processthe regenerated energy. Likewise, during a period T₂ in which thevoltage U-W of the U-phase relative to the W-phase becomes greater thanV₀, the drive signals A and F are rendered to assume the logic level"1", and the regenerated energy is processed via the transistors Q₁ andQ₆. For another period, similarly, the regenerated energy is processedvia two transistors. In FIG. 2, the symbol V_(H) denotes the potentialof the DC power source line V_(D), and G denotes the potential, 0 volt,of the ground line V_(E).

As was mentioned previously, the AC motor is not always placed in aregenerative condition in all of the moments during the decelerationmode but generally repeats the three modes, i.e., regeneration,circulation, and consumption. According to the conventional system inwhich the electric current is allowed to reversely flow from the DCpower source line to the AC power source in all of the moments duringthe deceleration mode as was mentioned in the foregoing, a very largeamount of electric power is consumed by the resistors R₁ and R₂.According to the conventional art, therefore, the resistors R₁ and R₂must be capable of handling large amounts of electric power. Sinceresistors for handling a large amount of power are large in size, theconventional apparatus for processing the regenerated energy requiresincreased space and is not adapted for being compactly constructed.

The object of the present invention is to solve the problem inherent inthe conventional apparatus described above with reference to FIG. 2.Namely, instead of using the outputs A to F produced by the phasedetector circuit 6, the apparatus of the invention uses the outputs A'to F' produced by the regeneration drive circuit 8 to drive thetransistors Q₁ to Q₆ for processing the regenerated energy so that theregenerated energy is returned to the AC power source only when the ACmotor is in a practically regenerative condition. The embodiment of theinvention is described below in further detail in conjunction with FIGS.3 to 5.

FIG. 3 is a circuit diagram of the drive circuit 4 and the AC motor 5and explains the principle for discriminating whether or not the ACmotor is in a regenerative condition. In FIG. 3, inductances L₁, L₂, andL₃ are provided for three phases of the three-phase AC motor 5. Theinductances L₁, L₂, and L₃ are connected to each of the phases of thedrive circuit 4 via resistors R₃, R₄, and R₅ for detecting currentdirections. PWM signals R⁺, S⁺, and T⁺ of three phases are applied tothe bases of the transistors Q₇, Q₉, and Q₁₁, respectively, and PWMsignals R⁻, S⁻, and T⁻ are, respectively, applied to the bases of thetransistors Q₈, Q₁₀, and Q₁₂. When the resistor R₃ for detecting currentdetects the current in the direction ○1 , the regenerated current mayflow through either a route ○A consisting of a diode D₄, the resistorR₃, the inductance L₁, the inductance L₂, the resistor R₄, and a diodeD₂ or a route ○B consisting of the diode D₄, the resistor R₃, theinductance L₁, the inductance L₃, the resistor R₅, and a diode D₃. Theregenerated current flowing through route ○A can be detected from thedirection ○1 of the current and the PWM signals R⁺ and S⁻ that assumethe logic level "0". The regenerated current flowing through route ○Bcan be detected from the direction ○1 of the current and the PWM signalsR⁺ and T⁻ that assume the logic level "0". Similarly, when the resistorR₃ for detecting the current detects the current in the direction ○2 ,the regenerated current may flow through either a route ○C consisting ofa diode D₅, the resistor R₄, the inductance L₂, the resistor R₃, and adiode D₁ or a route ○D consisting of a diode D₆, the resistor R₅, theinductance L₃, the inductance L₁, the resistor R₃, and the diode D₁. Theregenerated current flowing through route ○C can be detected from thedirection ○2 of the current and the PWM signals S⁺ and R⁻ that assumethe logic level "0". The regenerated current flowing through route ○Dcan be detected from the direction ○2 of the current and the PWM signalsT⁺ and R⁻ that assume the logical level "0".

Regenerated currents flowing through the resistors R₄ and R₅ fordetecting the directions of currents can also be detected by the samemeans as the one mentioned above.

In other words, the regenerated current flowing through the R-phase inthe direction ○2 can be detected by the following logical equation (1):##EQU1## where I_(R), I_(S), and I_(T), respectively, denote the logiclevels of currents that flow from the R-phase, the S-phase, and theT-phase of the PWM drive circuit into the AC motor 5, as is shown inFIG. 3. Referring to the right side of the above equation, the firstterm indicates that the regeneration detection signal of the R-phaseassumes the logic level "1" when R⁻, S⁺, and I_(R) assume the logiclevel "0" and when I_(S) assumes the logic level "1", i.e., theregeneration detection signal of the R-phase assumes the logic level "1"when the regenerated current flows through route ○C . The second termindicates that the detection signal of the R-phase assumes the logiclevel "1" when the regenerated current flows through route ○D .

Similarly, regeneration detection signals of the S-phase and the T-phasecan be obtained according to the following logical equations: ##EQU2##

When any one of the regeneration detection signals assumes the logiclevel "1", it can be said that the AC motor 5 is in a regenerativecondition.

FIG. 4 is a diagram showing the R-phase regeneration detection logiccircuit, which is a portion of the regeneration detection logic circuit7 of FIG. 1. In FIG. 4, an AND gate 11 produces R⁻.I_(R), and an ANDgate 12 produces S⁺.I_(S). An AND gate 13, which receives these outputsignals, then produces R⁻.I_(R).S⁺.I_(S). Similarly, an AND gate 14produces T⁺.I_(T), and an AND gate 15 produces R⁻.I_(R).T⁺.I_(T). Theoutputs of the AND gates 13 and 15 are input to an OR gate 16, whichthen produces the R-phase regeneration detection signal D_(R) given bythe equation (1).

By providing the same logic circuits as that of FIG. 4 for the S-phaseand T-phase, the regeneration signals D_(S) and D_(T) of the S-phase andT-phase can also be obtained as given by the equations (2) and (3).

FIG. 5 is a diagram illustrating in detail the regeneration drivecircuit 8 of FIG. 1. In FIG. 5, regeneration detection signals D_(R),D_(S), and D_(T) produced by the regeneration detection logic circuit 7are input via an OR gate 20 to first input terminals of AND gates 21,22, - - - , 26. Second input terminals of the AND gates 21, 22, - - - ,26 are served by drive signals A, B, C, - - - , F produced by the phasedetector circuit 6 (FIG. 1). Outputs A" to F" produced by the AND gates21 to 26 which are logical products of the drive signals A to F and theregeneration detection signals of the OR gate 20 serve as drive signalsthat represent a practical regenerative condition. The object of thepresent invention can also be accomplished when these signals A" to F"are directly applied to the bases of the transistors Q₁ to Q₆ forprocessing the regenerated energy shown in FIG. 1. According to theembodiment shown in FIG. 5, however, the potential rise of the DC powersource line V_(D) caused by the regenerated energy is simulated by usingan integration circuit, and drive signals are generated to drive thetransistors Q₁ and Q₆ for processing the regenerated energy for thefirst time when the potential of the DC power source line V_(D) israised by a predetermined voltage by the regenerated energy.

That is, the emitters of NPN transistors Q₁₃, Q₁₄, and Q₁₅ are commonlyconnected to a negative terminal of an operational amplifier 33, and thecollectors of these transistors are served with absolute values ofcurrents of the R-phase, S-phase, and T-phase of the AC motor 5 viaresistors R₆, R₇ and R₈. The bases of the transistors Q₁₃, Q₁₄, and Q₁₅are connected to outputs ○P , ○Q , and ○R of the AND gates 21, 23, and25. In a regenerative condition, as will be understood from theregenerated energy processing circuit 3 of FIG. 1 and the waveforms ofFIG. 2, one of the outputs ○P , ○Q , and ○R of the AND gates 21, 23, and25 always assumes the logic level "1". In a regenerative condition,therefore, any one of the transistors Q₁₃, Q₁₄, and Q₁₅ is necessarilyrendered conductive, and the regenerated current is supplied to thenegative terminal of the operational amplifier 33. An integrationcircuit is constituted of a capacitor C₂ and a resistor R₉ connected inparallel with the operational amplifier 33, a bias resistor R₁₀connected between the positive terminal of the operational amplifier 33and the ground, and the resistor R₆, R₇, or R₈ inserted in each of thephases. Therefore, the operational amplifier 33 produces an integratedvalue of the regenerated current. The integrated value is input to acomparator circuit 34. As the integrated value reaches a firstpredetermined value, for example, 10 volts, the output of the comparatorcircuit 34 is switched from the logic level "0" to the logic level "1".The output of the comparator circuit 34 is input to the first inputterminals of AND gates 27 to 32, whose second terminals are served bythe outputs of the AND gates 21 to 26. The outputs of the AND gates 27to 32 serve as drive signals A' to F' which are applied to the bases ofthe transistors Q₁ to Q₆ for processing the regenerated energy ofFIG. 1. The outputs of the AND gates 27 to 32 are further fed back tothe negative terminal of the operational amplifier 33 via an OR gate 35and a negative feedback resistor R₁₁. As the output voltage of theoperational amplifier 33 decreases to a second predetermined value, forinstance, 3 volts, the output of the comparator circuit 34 assumes thelogic level "0" and, hence, the drive signals A' to F' assume the logiclevel "0". Therefore, the regenerated energy is not returned to the ACpower source even though it exists. As the output voltage of theoperational amplifier rises again to exceed the first predeterminedvalue, two signals assume the logic level "1" among the signals A" to F"as long as a regenerative condition is established. Therefore, two drivesignals assume the logic level "1" among the drive signals A' to F', andthe regenerated energy is returned to the AC power source via theregenerated energy processing circuit 3 of FIG. 1. By suitably selectingthe ratio of the resistance R₆, R₇, or R₈ constituting the integrationcircuit to the negative feedback resistance R₁₁, the operationalamplifier 33 produces an integrated value for simulating the potentialrise of the DC power source line V_(D) caused by the regenerated energy.

According to the circuit constitution shown in FIG. 5, the regeneratedenergy is not returned to the AC power source at all times whenever aregenerative condition is established but is returned to the AC powersource for the first time when the voltage of the DC power sourcebecomes greater than a predetermined value due to the regeneratedenergy. Therefore, electric power is consumed in reduced amounts by theprotection resistors R₁ and R₂.

The consumption of electric power by the protection resistors R₁ and R₂can be greatly reduced even when the signals A" to F" produced by theAND gates 21 to 26 are applied as drive signals to the bases of thetransistors Q₁ to Q₆, as was mentioned earlier, compared with when thetransistors Q₁ to Q₆ are driven by the signals A to F produced by thephase detector circuit 6 as is the case in the conventional art.

In the foregoing was mentioned an embodiment of the apparatus forprocessing the energy regenerated by the three-phase AC motor. Theinvention, however, should in no way be limited thereto only but can beadapted to any other AC motor. In this case, it will be easilyunderstood by those skilled in the art that the rectifier circuit, theregenerated energy processing circuit, the regeneration detection logiccircuit, and the regeneration drive circuit should be designed to suitthe type of AC motor.

According to the present invention as described in the foregoing, thesemiconductor switches for processing the regenerated energy arerendered conductive only when a regenerative condition is established toreturn the regenerated energy to the AC power source. Therefore,electric power is consumed in reduced amounts by the resistors thatprotect the semiconductor switches for processing the energy regeneratedby the AC motor. Accordingly, resistors constructed for handling a smallamount of electric power may be employed, and the apparatus forprocessing the regenerated energy can be constructed so as to have agreatly reduced size.

We claim:
 1. An apparatus for processing energy regenerated by an ACmotor which comprises:a rectifier circuit (2) for supplying a directcurrent to the lines of a DC power source by rectifying an alternatingcurrent supplied from an AC power source; a drive circuit (4) includingAC motor driving semiconductor switches (Q₇ to Q₁₂) connected across thelines of said DC power source, said semiconductor switches beingrendered conductive upon the receipt of a PWM signal when the AC motoris to be driven so as to supply the electric current from the lines ofsaid DC power source to each of the phases of said AC motor; aregenerated energy processing circuit connected across the lines of saidDC power source, including regenerated energy processing semiconductorswitches (Q₁ to Q₆) for returning the energy regenerated by said ACmotor to said AC power source, and resistors (R₁ and R₂) for protectingsaid regenerated energy processing semiconductor switches; currentdirection detectors (10₁, 10₂, and 10₃) for detecting the direction ofthe current flowing through each of the phases of said AC motor; aregeneration detection logic circuit (7) for producing a regenerationdetection signal when said AC motor driving semiconductor switches arenonconductive and when the direction of the current detected by thecurrent direction detectors is opposite to the direction of the currentwhen said AC motor is driven; and a regeneration drive circuit (8) fordriving said regenerated energy processing semiconductor switchesresponsive to said regeneration detection signal.
 2. An apparatus forprocessing the regenerated energy as set forth in claim 1, wherein saidAC motor has a plurality of phases and said regeneration detection logiccircuit (7) is equipped with a plurality of phase regeneration detectionlogic circuits for detecting the regenerative conditions of each of saidplurality of phases.
 3. An apparatus for processing the regeneratedenergy as set forth in claim 2, wherein said AC motor drivingsemiconductor switches are provided with a plurality of phase drivingsemiconductor switches for driving a plurality of phases of said ACmotor and each of the phase driving semiconductor switches is providedwith a transistor for energizing the motor and a transistor forde-energizing the motor.
 4. An apparatus for processing the regeneratedenergy as set forth in claim 3, wherein each of said phase regenerationdetection logic circuits receives a PWM signal applied to a transistorfor de-energizing said motor that is included in a semiconductor switchfor driving the corresponding phase, a PWM signal applied to atransistor for driving said motor that is included in a semiconductorswitch for driving phases other than the corresponding phase, andsignals that indicate the direction of the current flowing through eachof the phases of said AC motor and produces a phase regenerationdetection signal that indicates whether or not the corresponding phaseis in a regenerative condition.
 5. An apparatus for processing theregenerated energy as set forth in claim 4, wherein said regenerationdetection logic circuit produces said regeneration detection signal whenat least one of said phase regeneration detection signals indicates aregenerative condition in the corresponding phase.
 6. An apparatus forprocessing the regenerated energy as set forth in claim 5, wherein saidregeneration drive circuit is provided with an integration circuit whichsimulates the potential of the line of said DC power source and acomparator which compares the output voltage of said integration circuitwith a predetermined value and said regeneration detection signal isapplied to said semiconductor switches for processing the regeneratedenergy when the output voltage of said integration circuit exceeds saidpredetermined value.